1. Field of the Invention
The present invention relates to a cruise control apparatus for vehicle. Priority is claimed on Japanese Patent Application No. 2004-256856, the content of which is incorporated herein by reference.
2. Description of Related Art
There is a cruise control apparatus that, for example, detects the existence of a preceding vehicle by using an in-vehicle radar device. When a preceding vehicle is detected, the cruise control apparatus controls speed within a target speed set beforehand so as to keep a predetermined inter-vehicle distance. When a preceding vehicle is not detected, the cruise control apparatus controls speed so as to maintain a target speed (e.g., see Japanese Unexamined Patent Application, First Publication No. 2004-130880).
This type of cruise control apparatus switches and processes two types of controls in accordance with the speed of the subject vehicle, one of which is a low speed following control that, in a relatively low speed region such as, for example, when driving in congested traffic, can stop and start the subject vehicle while following an appropriate operating state including stationary state of the preceding vehicle, and another control is an adaptive cruise control that, in a relatively high speed region, follows the preceding vehicle without assuming stopping of the preceding vehicle.
In the cruise control apparatus according to the prior art, during adaptive cruise control in the relatively high speed region, a target inter-vehicle distance is set in accordance with a predetermined time headway (time after passing through a point with one vehicles until the following vehicles arrive at the same point) and speed, and during low speed following control, a predetermined target inter-vehicle distance to be maintained when the subject vehicle stops due to stopping of the preceding vehicle is set. In order to prevent an abrupt change in the target inter-vehicle distance accompanying a switch of control in speed regions that is switching between adaptive cruise control and low speed following control, a target inter-vehicle distance is obtained by smoothly extending the target inter-vehicle distance set in adaptive cruise control to the low speed following control region side, even in a speed region in which low speed following control is applied and that is close to a speed region in which adaptive cruise control is applied. Moreover, in this case, in an extremely low speed region close to zero speed, the target inter-vehicle distance is obtained by smoothly connecting a target inter-vehicle distance, that is obtained by extending from the speed region in adaptive cruise control, to a predetermined target inter-vehicle distance maintained when the subject vehicle stops in accompanying stoppage of the preceding vehicle in low speed following control.
However, when the target inter-vehicle distance in low speed following control is set simply by smoothly extending the target inter-vehicle distance set in adaptive cruise control to the low speed region side, the target inter-vehicle distance becomes excessively short, particularly in the extremely low speed region. This leads to problems such as, for example, excessive deceleration being required when the subject vehicle decelerates in accompanying an abrupt stoppage and the like of the preceding vehicle, or it may become impossible to suitably react to deceleration of the preceding vehicle.
The present invention is realized in view of the above, and aims to provide a cruise control apparatus for vehicle that can operate suitable deceleration when following appropriate operating status including stoppage of the preceding vehicle.